import java.util.Scanner;

import static java.lang.Math.*;
public class Circle {
    public  int radius = 5;
    public double findArea(){
        double b = 2*pow(radius,2)*PI;
        return Math.round(b*100.0)/100.0;

    }

    public static void main(String[] args) {
       Circle c =  new Circle();
        Scanner scan = new Scanner(System.in);
        int name = scan.nextInt();
        c.radius = name;
        scan.close();
       System.out.println(c.findArea());

    }
}
